In blasting operations, various devices are used to transmit a blast signal from a remote initiation location to explosives in a borehole. These devices include detonating cord, safety fuses, energy transmission tubes, blasting caps and various connectors arranged in such a manner as to detonate explosives in a desired sequence and pattern. In nonelectric systems, delay elements may be interposed along signal transmission lines on the surface or in the boreholes to achieve sequential initiation of explosive charges.
In a typical arrangement, trunklines carry the blast signal from an initiator to downlines or to surface delay devices. Both trunklines and downlines are lengths of detonating cord or other signal transmitting devices. The trunkline is the portion of the transmission line on the surface, connecting boreholes. A downline is connected to a trunkline and extends into a borehole. The downline transmits the signal from the trunkline or surface delay element to the explosive in the borehole. The downline may also be attached to delay devices in the boreholes and/or to instantaneous blasting caps in the borehole.
The use of delay devices to detonate explosives in a predesigned pattern at predetermined times can be useful to achieve the desired breakage of rock. This is particularly true when the explosives within a borehole are "decked", that is, loaded in explosive sections that are detonated at different times. Delay devices also help to reduce the noise and vibration common to blasting operations which is important in light of governmental regulations and complaints from nearby residents. Due to these advantages, the industry has made wider use of delay devices.
To provide different delay periods downhole and to accommodate holes of varying lengths, it has been common practice to place a desired delay element on one end of a single transmission device. Typically a series of signal transmission tubing lengths are provided for each delay. For example, a 25 millisecond delay cap may be attached to various lengths of single transmission tubing, e.g., 10 feet, 15 feet, 20 feet and 25 feet. Unfortunately, this requires a large inventory of both different delay elements and different lengths of transmission tubing.
There is a continuing need to provide a reliable, simple, yet versatile system which will allow connection of explosive charges in a pattern. The present modular system has the advantage of providing a system which is easy to use while permitting easy variation of blasting patterns. The present invention also permits a substantial reduction in inventory by accommodating a great variety of combinations from a few elements. The present system also has the advantage that the signal tubing can function as both the downline and the trunkline. Further, the system can be utilized to provide multiple pathways for detonation signals between boreholes, thus increasing reliability of detonation.